Thermocouple test cup and cupholder

ABSTRACT

An expandable test mold is provided for obtaining data with a high degree of reproducibility on molten materials, especially metal alloys, as the material solidifies and continues to cool within the mold. The mold is preferably cup-shaped, and the data such as that for a cooling curve are taken by a thermocouple which extends into the cup and terminates substantially centrally thereof. The high incidence of reproducible results is primarily due to a continuous, smooth, break-free, internal, integral refractory single or multiple layer coating which entirely covers at least the length of the thermocouple sensing means extending within the cup and preferably the walls and base of the cup as well. Such a coating, free of curtaining and other nonuniformities, can be obtained by first filling the cup with an aqueous slurry of a particulate refractory material and then inverting the cup to allow the slurry to drain for a time sufficient to form the continuous, smooth coating over the entire interior of the mold and the thermocouple sensing means but without losing its ability to flow. Thereafter, the cup is set upright and coating allowed to dry. This process may be repeated to provide additional layers to the coating in order to accelerate the cooling rate of the sample. Optionally, the base of the cup is shaped to place the electro-conducting leads of the thermocouple in predetermined, polarized position so that the cup can be seated in a cupholder in only one, correctly polarized position.

United States Patent 91 Jeric 11] 3,844,172 [451 Oct. 29,1974

[ THERMOCOUPLE TEST CUP AND CUPl-IOLDER [76] Inventor: Joseph M. Jeric, 104 Maple Hill Dr.,

South Russell, Ohio 44022 22 Filed: Jan. 14,1972

21 Appl. No.: 217,731

[52] US. Cl 73/354, 73/359, 73/DIG. 9 [5l] Int. Cl. G0lk 13/12 [58] Field of Search 73/359, 354, DIG. 9, 17 R,

73/355, 15 R, 15 A, 15 B; 136/233, 234

Primary Examiner-Richard C. Queisser Assistant Examiner-Denis E. Corr Attorney, Agent, or Firm-Bosworth, Sessions & McCoy [5 7 ABSTRACT An expandable test mold is provided for obtaining data with a high degree of reproducibility on molten materials, especially metal alloys, as the material solidifies and continues to cool within the mold. The mold is preferably cup-shaped, and the data such as that for a cooling curve are taken by a thermocouple which extends into the cup and terminates substantially centrally thereof. The high incidence of reproducible results is primarily due to a continuous, smooth, breakfree, internal, integral refractory single or multiple layer coating which entirely covers at least the length of the thermocouple sensing means extending within the cup and preferably the walls and base of the cup as well. Such a coating, free of curtaining and other nonuniformities, can be obtained by first filling the cup with an aqueous slurry of a particulate refractory material and then inverting the cup to allow the slurry to drain for a time sufficient, to'form the continuous, smooth coating over the entire interior of the mold and the thermocouple sensing means but without losing its ability to flow. Thereafter, the cup is set upright and coating allowed to dry. This process may be repeated to provide additional layers to the coating in order to accelerate the cooling rate of the sample. Optionally, the base of the cup is shaped to place the electro-conducting leads of the thermocouple in predetermined, polarized position so that the cup can be seated in a cupholder in only one, correctly polarized position.

7 Claims, 5 Drawing Figures THERMOCOUPLE TEST CUP AND CUPHOLDER BACKGROUND OF THE INVENTION In order to determine the amount of various constituents in a molten metal alloy, such as before casting the alloy, it has been the practice to cast a test ingot which, after cooling and solidification, was chemically analyzed. The time required for the chemical analysis alone was frequently much too long and delayed casting of the alloy with resulting poor production rates. Alternatively, castings were made with the expectation that the composition was satisfactory. Later, when analysis showed the alloy not to be within specifications, the castings prematurely made had to be scrapped.

Inasmuch as cooling curves of metal alloys reveal significant information as to their metallurgical make-up and cell structure foundry men next resorted to plotting cooling curves derived on test samples of molten alloys to determine various characteristics of the alloys and particularly what adjustments might be necessary to bring the alloy composition within permissible specified limits. This technique provided an immediate assessment and indicated in short order what remedial adjustments might be required.

A cooling curve of a metal alloy is informative, since solidification and cooling of the alloy normally takes place over a temperature range. Both the temperature at the start of the solidifcation (liquidus) and the temperature at complete solidification (solidus) and eutectic temperature varies with the composition of the alloy. Each of these temperatures as well as the magnitude of the difference between them can reveal much to those skilled in the art concerning the composition and/or the micro cell structure of the alloy. For example, by simply observing the liquidus break in a cooling curve of a molten alloy sample, a melter may know what adjustments should be made to bring the alloy within specification limits.

Similarly, a study of cooling characteristics of molten grey iron permits a determination of the carbon equivalent value of the resulting cast iron, that is, the amount of carbon present plus one-third of the amount of silicon present. The carbon equivalent test is based on a measurement of the liquidus arrest temperature as a sample of the molten iron alloy solidifies. The use of cooling curves in the field of iron castings is described by the following magazine articles: Grey Cast Iron Control by Cooling Curve Techniques by Redshaw, Payne and Hoskins, in New Technology, page 91, February, I962; and Rapid Control Test for Carbon Equivalent", by Krause in Foundry, page 201, May, I962. However, cooling curves can be used for still other purposes, such as in a study of the effect of cooling rates on the grain sizes of alloys, such as magnesium-aluminum-zinc alloys, or commercial cast irons as described by .I. E. Barton s report to Malleable Founders Society, Mar. 16-18, I971.

Test cups have been suggested for receiving a sample of metal alloy outside of the furnace in which it is being processed and for measuring the temperature of the charts to indicate the temperatures at which temperature arrests or other phenomena occur.

A critical factor in the use of such test cups is their reliability and especially their ability to provide reproducible results. Test cups previously used are basically sand molds prepared by standard foundry castings and, as such, are fragile and break easily, either in handling or while in use.

More significantly, the thermocouple is particularly subjected to severe conditions during use. An alloy cools and solidifies in a test cup from the periphery of the cup toward its center. This requires thermocouple sensing means to be stationed substantially at the center in order to sense the temperature of a still molten alloy until the solidus is finally reached for the entire test sample. However, this subjects the thermocouple to an ever increasing, radially inwardly directed pressure. Especially at the point of solidus, the pressure on a thermocouple is appreciable and can electrically short-circuit its function or otherwise cause the thermocouple to report false readings. For example, molten metal can force its way into a thermocouple probe and create unintended thermocouple junctions leading to false readings.

On the other hand, if a thermocouple is encased to shield it from electrical short circuits as a result of pressure from the solidifying melt, sensitivity and accuracy of the thermocouple are seriously hampered such that incorrect readings are again produced.

SUMMARY OF THE INVENTION The present invention provides a test cup that is capable of a high degree of accurate, reproducible results. The cup is not only less apt to fracture in use or handling but protects a thermocouple against the pressure and electrical shortcircuiting engendered by a solidifying alloy without lessening the sensitivity or accuracy of the thermocouple. I

These improved results are obtained by a continuous, smooth, break-free, internal, integral refractory coating, such as of Alundum, which entirely covers at least the thermocouple sensing means, including the normally exposed electrical leads forming the hot junction, and preferably the inside walls and base of the cup as well. The integral coating tends to insure uniform cooling rates and reinforces the cup walls against breakage while also protecting all parts of the thermocouple without diminishing its accuracy or effectiveness. In the preferred embodiment, a tip of the thermocouple insulating tube is free of sharply angled edges to promote a uniform coating and inhibit potential leaks at breaks in the coating otherwise occasioned by sharp edges.

The present invention also contemplates a cupholder in which preferably both the test cup and the holder are designed to seat together only in a predetermined, polarized electrical connection.

The refractory coating of Alundum or equivalent is preferably applied to the interior of a test cup by a process in which the cup is initially filled with a slurry of the particulate refractory material, drained in an inverted position for a time sufficient to form a continuous, smooth, break-free coating, but then allowed to dry while in an upright position. A coating comprising melt as it solidifies and continues to cool by means of one or more layers may be supplied in this manner.

a thermocouple projecting into the test cup. Temperature values sensed by the thermocouple preferably are traced by a recording pyrometer in a known manner on BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the present test cup and cupholder seated in a test stand which may be used for connecting the thermocouple leads to a recording pyrometer or the like;

FIG. 2 is an enlarged, vertical, center section of the test cup of FIG. 1 and illustrates an internal, integral refractory coating;

FIG. 3 is a bottom plan view of FIG. 2 taken on the plane of the line 3-3;

FIG. 4 is an enlarged view of a tip of a thermocouple probe prior to coating and shows a beveled end of the insulating thermocouple tube for the thermocouple leads; and

FIG. 5 is an enlarged, vertical, center section of the cupholder of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT ing the cup 10 and cupholder 11 while a test is being conducted.

Referring more particularly to the cup and cupholder, the cup 10 includes a tubular, heat-resistant mold open at one end to expose an inner wall 10a and closed at the other end by an integral base 10b. The cup may be a conventional foundry casting of sand and a binder, such as phenol formaldehyde. The cup has a central, axially extending aperture 16 to receive a thermocouple probe comprising an electrically insulating tube 17 having spaced passages 18 (FIG. 4) through which thermocouple leads 20 and 21 extend and are twisted together beyond the upper end of tube 17 as at 22 to form a hot junction. Tube 17 may be formed from fused quartz or sillmanite. The leads 20 and 21 are of conventional, known materials for this purpose, such as 22 gauge C hromel-Alumel wires. However, other known thermocouple leads can be used such as wires of platinum and platinum with [0 per cent or 13 per cent rhodium alloy, or of platinum and platinum with 15 per cent iridium.

A coating of Alundum 23 completely covers inner wall 10a of the cup, floor 10b of the base, the length of tube 17 extending within cup 10, and the twisted ends of hot junction 22 of the thermocouple, such that a hot alloy melt contacts only refractory coating 23 within the cup. In place of Alundum, other refractory coatings may be used such as silica, burnt dolomite, and the like.

However, my present experience indicates that Alundum is superior to others in forming the coating for the test cup.

As indicated, a continuous, break-free coating must be obtained. It has been found that sharp edges, short bends and the like inhibit realization of a continuous coating. Prior to drying the coating tends to separate across a sharp edge, probably because of surface tension. The edge then penetrates through the dried coating and provides routes of leakage for a molten alloy. This tendency is particularly critical around the thermocouple hot junction and at the base connection of the thermocouple tube with the test cup. Electrical short circuits are most apt to occur at these areas due to breaks in the coating 23 and/or the inward radial pressures of the solidifying hot alloy melt, expecially when the solidus temperature is reached, the latter being important to the cooling curve data.

In the present cup, surface angles of more than 60 are reduced or accounted for by a particular process of coating the cup. For example, the flat tip of an insulating twoholed tube for the thermocouple leads is normally cut at right angles to its sides. This area is particularly prone to weakness and vulnerable to breaks in the coating 23 because of the sharp 90 angled edge. The undesirable result is often leakage of a molten melt into the tube and its internal passages, and short-circuiting of the thermocouple. In the present test cup, this is avoided by relieving the sharp edge normally occuring at the end of the tube, as by beveling it as illustrated at 17a in FIG. 4, so that no surface angle remains greater than about 60. This area of tube 17 is then evenly and easily coated.

The intersection of thermocouple tube 17 with floor 10b of the base of the cup is another area where leakage is apt to occur and short circuit the thermocouple or otherwise cause it to provide inaccurate readings. A preferred technique in applying the coating not only provides a continuous, smooth, break-free, integral refractory coating but creates a strengthening and protective fillet 23a of the coating which surrounds and reinforces the base of thermocouple insulator tube 17. A similar fillet 23b forms as a result of this application technique at the intersection between wall 10a and floor 10b of the test cup.

In the preferred coating process, cup 10 is completely filled to the brim with an aqueous slurry of the particulate refractory material forming the coating. The cup is then inverted but only for a relatively brief time to permit the excess slurry to drain leaving a con tinuous, smooth, break-free, integral coating over the entire interior of the cup and the thermocouple probe. Before the slurry loses its ability to flow, the cup 10 is set upright and the coating allowed to dry. Before com pletely drying, the slurry flows downwardly slightly, and the coating 23 on the vertical surfaces becomes uniform and smooth. Also desirable protective and strengthening fillets 23a and 23b are simultaneously formed.

A particularly desirable feature of this process is that the flow of coating 23 downward on the twisted tip 22 of the thermocouple junction that extends beyond the end of insulating tube 17 is greater than along the sides of tube 17. As a result a relatively thin coating remains on the junction to the benefit of its sensitivity while a reinforcing amount of coating is deposited at the end of tube 17 through which the wires appear to enable it better to withstand the pressures of the cooling sample.

A preferred form of thermocouple comprises a conventional bright annealed non-welded junction. As is well known, the effective point of temperature sensing of such a junction is the twist at which the wires first are in contact, l.e., the first twist beyond the end of tube 17. The downward flow of coating comprehended by this invention on and along such a junction advantageously results in a reduced coating thickness at the twist that constitutes the effective point of temperature sensing.

In one run, for example, a test cup of the present invention measured about L inches in outside diameter, about 1.25 inches in inside diameter, and had a height of about two inches from floor b to the open end of the cup. The cup was filled with an aqueous slurry containing 74 per cent by weight of alundum. After inverting the cup, the slurry was allowed to drain for 12 to 14 seconds. Then the cup was set upright and allowed to dry at room temperature. A coating of Alundum averaging about 6 mils thick was formed on the vertical surfaces.

This invention comprehends cups having refractory coatings comprised of one or more layers. The process described above provides a single layer coating. Multiple layer coatings are obtained by repeating this process for each additional layer desired.

The advantage of the multiple layer refractory coatings herein disclosed is that they provide a convenient and effective way to control and to adjust the cooling rates of the samples held by coated cups. For example, it has been found that the cooling rate increases as the number of layers of Alundum applied in accordance with this invention is increased. The slowest rate is achieved by a single layer coating and although the coating thickness may have some effect on the rate, the number of layers seems to be more determinative of cooling rate. The ability to adjust the rate by this method is predictable and repeatable. It is particularly advantageous when the coated cups are being used in micro cell structure studies and to study the effect of cooling rates on grain size. The advantage of an adjustable and controllable cooling rate through multiple layer coatings is gained without sacrifice of the other advantages described above.

Thermocouple leads and 21 may be suitably connected to any conventional equipment desired, such as a recording pyrometer. However, the present cup and cupholder are designed to seat together in a predetermined polarized connection. Referring particularly to FIGS. 2 and 3, cup 10 has a downward extension 24 including a continuation of aperture 16. Extension 24 has two opposed flats or lands 25 and 26 (FIG. 3) generally parallel to each other and located unequal radial distances from the central aperture 16 and central longitudinal axis of cup 10. Lands 25 and 26 define electrojunction areas for union between thermocouple leads.

20 and 21 and cupholder 11. After thermocouple lead 20 leaves the tube 17, for example, it extends radially along the outside of extension 24 and terminates on flat 25, while thermocouple lead 21 similarly terminates on flat 26.

Cupholder 11 includes a tubular housing 27 of electrical insulating material having an open end adapted to receive extension 24 of cup 10. Bottom end strips 28 secure a rectangular support plate 30, also of electrical insulating material, in position by any suitable cement 31, such as phenol formaldehyde or epoxy resins. Plate 30 has a downwardly extending tab 32 to which electro-conducting strips 33 and 34, one of Alumel and the other of Chromel alloys, are fixed by brass screws 35. Two L-shaped plug prongs 36 and 37, one of Alumel and the other of Chromel alloys, are electrically connected to strips 33 or 34 of like metal and covered by an electrically insulating cement 38, such as phenol formaldehyde or a rubber-based cement.

Strips 36 and 37 are spaced at different radial distances inwardly of housing 27 and positioned so that they correspond to the eccentricity of the two lands 25 and 26 of cup 10 on which the two thermocouple wires 20 and 21, respectively, lie. Strip 36, being spaced-inwardly a greater distance, is designed to contact land 26 and lead 21, while strip 37 contacts land 25 and lead 20. Strips 36 and 37 are of suitable gauge to impart resilient bending. As located within the housing 27, the strips are also spaced sufficiently away from the housing so that they are free to bend a limited amount, for example, toward and away from the axis of the cupholder 11.

The eccentricity of the base of cup 10, as described, in combination with the eccentricity of strips 36 and 37 in the cupholder adapt the two parts to fit together in only one way and to polarize the two different leads 20 and 21 of the thermocouple with the matching metals of L-shaped strips 36 and 37 in the cupholder. In this way, the eccentricity of the mating parts polarizes the connection of the thermocouple hot juncture 22 in the test cup to an instrument to which the thermocouple current is transmitted. Terminal screws 35 join insulated leads 40 to strips 33 and 34. The leads 40 may be made of compensating metal, as is known in the art, when strips 33 and 34 comprise noble metal. Leads 40 connect the thermocouple to any desired instrument.

The unbroken protective sheath of refractory material along the entire interior of the cup provides more uniform cooling rates, reduces the likelihood of serious fracture of the cup and, most significantly, protects the thermocouple probe against shorting out or providing false signals due to leakage of a melt into parts of the probe. Yet the thermocouple junction is not so covered that its sensitivity or accuracy is impaired. As a direct result, the present test cup has a high degree of reliability with reproducible results occurring in nearly per cent or more of a series of runs. The construction of the test cup insures that the proper polarity of thermocouple connections with a measuring instrument is always obtained.

While the foregoing describes a presently preferred embodiment, it is understood that the present invention may be practiced in still other forms within the scope of the following claims.

What is claimed is:

1. The process for providing a coating on the inside of a thermocouple test cup and on a thermocouple sensing means extending thereinto comprising the steps of l. filling the cup with an aqueous slurry of a particulate refractory material,

2. inverting the cup and allowing the slurry to drain for a time sufficient to form a continuous, smooth, break-free, integral layer of coating over the entire inside surface of the cup and the surface of the thermocouple sensing means,

3. setting the cup upright while said coating still retains an ability to fiour, and

4. allowing the coating to dry.

2. The process for providing a multiple layer coating on the inside of a thermocouple test cup and on a thermocouple sensing means extending thereinto comprising repeating all the series of steps according to claim 1 as many times as layers of coating to be provided.

3. The process for controlling and adjusting the cooling rate of a sample of molten metal alloy comprising the steps of 1. providing a thermocouple test cup having a thermocouple sensing means extending thereinto,

2. coating the inside of said cup and said thermocouple sensing means extending thereinto with a layer of refractory material in accordance with all the steps of claim 1, and

3. repeating step (2) to increase the cooling rate.

4. An expendable test mold for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said mold comprising a heat-resistant cup member having walls and a connecting base a thermocouple sensing means extending through the cup member and terminating substantially centrally thereof, and

a continuous, smooth, break-free, internal, integral refractory coating substantially entirely covering the walls and base of said cup member and the length of said thermocouple means extending within the cup member, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone.

5. The test mold of claim 4 in which said refractory coating is an air setting material comprised substantially of aluminum oxide.

6. An expendable test cup for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said cup comprising a heat-resistant cup member having walls and a connecting base,

a thermocouple sensing means extending through the cup member and terminating substantially centrally thereof, comprising a pair of electroconducting wires contained within and insulated from one another by an electrically insulating probe member extending within the cup member, said wires projecting from an end portion of the probe member and joined to one another to form a hot junction, said end portion of said probe being shaped to avoid surface angles of more than about degrees, and

a continuous, smooth, break-free, internal, integral refractory coating substantially entirely covering the walls and base of said cup member and the length of said probe member extending within the cup member including said end portion and said hot junction, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone.

7. An expendable test cup for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said cup comprising a heat-resistant cup member having walls and a connecting base and comprising sand and a binder,

a theremocouple sensing means extending through the cup member and terminating substantially centrally thereof, and

a continuous, smooth, break-free, internal, integral refractory coating of an air setting material comprised substantially of aluminum oxide, said coating substantially entirely covering the walls and base of said cup member and the length of said thermocouple means extending within the cup member, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone.

* l l= =l il-UNITED STATES PAT NT OFFICE CERTIFICATE OF- CORRECTION Patent No. $844,172 Dated October 29, 1974 Inventor(s) I d p JeriC I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 65, change "supplied" .to -applied-- Column 6, line 56 change "flour" to --flow--- Column 8, linev2l, change "theremocouple" to -thermocouple Signed and sealed this 21st day of .Januaiy 1975.

(SEAL) v Attest:

- MCCOY M. GIBSON 'JR. C MARSHALL DANN Attesti'ng Officer Commissioner of Patents 1 FORM PO-IOSO (10-69) uscoMM-Dc eoave-pas I I 9 ,5. GOVERNMENT PRINTING OFFICE: I959 0-366-334 1 :'IIJNITED STATES PATENT OFFICE CERTIFICATE OF; CORRECTION Patent No. 3,844 172 Dated October 29, 1974 Inventor(s) d P Jeric It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

a Column 2, line- 65, change "supplied".to -appl Led-- Column 6, line 56 change "flour" to --flow-- Column 8, lineu2l V change "theremocouple" to thermocouple Signed sealed this 21st day of January 1975.

(SEAL) Attest: I

- McCOY M. GIBSON JR, C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM po'wso USCOMM-DC moan-ps9 I v U.S. GOVERNMENT PRINTING QFFICEZ l9, 0-355'33 

1. The process for providing a coating on the inside of a thermocouple test cup and on a thermocouple sensing means extending thereinto comprising the steps of
 1. filling the cup with an aqueous slurry of a particulate refractory material,
 2. inverting the cup and allowing the slurry to drain for a time sufficient to form a continuous, smooth, break-free, integral layer of coating over the entire inside surface of the cup and the surface of the thermocouple sensing means,
 3. setting the cup upright while said coating still retains an ability to flour, and
 4. allowing the coating to dry.
 2. inverting the cup and allowing the slurry to drain for a time sufficient to form a continuous, smooth, break-free, integral layer of coating over the entire inside surface of the cup and the surface of the thermocouple sensing means,
 2. coating the inside of said cup and said thermocouple sensing means extending thereinto with a layer of refractory material in accordance with all the steps of claim 1, and
 2. The process for providing a multiple layer coating on the inside of a thermocouple test cup and on a thermocouple sensing means extending thereinto comprising repeating all the series of steps according to claim 1 as many times as layers of coating to be provided.
 3. The process for controlling and adjusting the cooling rate of a sample of molten metal alloy comprising the steps of
 3. repeating step (2) to increase the cooling rate.
 3. setting the cup upright while said coating still retains an ability to flour, and
 4. allowing the coating to dry.
 4. An expendable test mold for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said mold comprising a heat-resistant cup member having walls and a connecting base a thermocouple sensing means extending through the cup member and terminating substantially centrally thereof, and a continuous, smooth, break-free, internal, integral refractory coating substantially entirely covering the walls and base of said cup member and the length of said thermocouple means extending within the cup member, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone.
 5. The test mold of claim 4 in which said refractory coating is an air setting material comprised substantially of aluminum oxide.
 6. An expendable test cup for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said cup comprising a heat-resistant cup member having walls and a connecting base, a thermocouple sensing means extending through the cup member and terminating substantially centrally thereof, comprising a pair of electro-conducting wires contained within and insulated from one anOther by an electrically insulating probe member extending within the cup member, said wires projecting from an end portion of the probe member and joined to one another to form a hot junction, said end portion of said probe being shaped to avoid surface angles of more than about 60 degrees, and a continuous, smooth, break-free, internal, integral refractory coating substantially entirely covering the walls and base of said cup member and the length of said probe member extending within the cup member including said end portion and said hot junction, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone.
 7. An expendable test cup for obtaining data during and controlling the rate of cooling and solidification of molten material therein, said cup comprising a heat-resistant cup member having walls and a connecting base and comprising sand and a binder, a theremocouple sensing means extending through the cup member and terminating substantially centrally thereof, and a continuous, smooth, break-free, internal, integral refractory coating of an air setting material comprised substantially of aluminum oxide, said coating substantially entirely covering the walls and base of said cup member and the length of said thermocouple means extending within the cup member, said coating and said cup member having substantially different thermal characteristics whereby the coating modifies the rate of cooling of the sample provided by the cup alone. 